applicationDid

applicationDid is a naming convention used in Apple's app development to refer to a group of delegate callbacks that begin with the phrase “applicationDid.” These methods are part of the app lifecycle and are called by the system in response to changes in an application's state. There is no single method called applicationDid; instead, multiple methods share this prefix to signal that a state transition has completed.

Two common examples are applicationDidBecomeActive(_:) and applicationDidEnterBackground(_:). The former is invoked when the app moves from an inactive to an active state, and it is typically used to restart tasks, refresh the user interface, or resume paused activities. The latter is called when the app enters the background, and it is commonly used to release shared resources, save user data, and invalidate timers so the app can run efficiently while not in the foreground.

In addition to the applicationDid prefix, there are other lifecycle callbacks with different prefixes, such as applicationWillResignActive(_:) and applicationWillEnterForeground(_:), which signal upcoming transitions rather than completed ones. Together, these methods give developers hooks to manage app behavior during start, pause, backgrounding, foregrounding, and termination.

Implementation typically occurs in the app’s delegate object (for iOS, the AppDelegate conforming to UIApplicationDelegate; for macOS, a similar delegate). Developers implement the relevant methods to maintain state, ensure data integrity, and optimize resource usage. The availability and naming of these methods can vary slightly between platforms and OS versions, but the general concept of lifecycle callbacks with an applicationDid prefix remains consistent.